Summary of Work: Ref-1 is the mouse homologue of Drosophila Rrp1 and exonuclease III. It was first identified and purified on the basis of its DNA-repair nuclease activity, and later identified as a cellular factor capable of stimulating DNA binding of the transcription factors fos and jun. The stimulation provided by Ref-1 is associated with its reducing potential; reduced Ref-1 stimulates oxidized fos/jun, but oxidized Ref-1 does not. These two distinct functions have been mapped to two separate regions of the Ref-1 protein. The redox function requires the amino-terminal fragment including residues 36-64, while the nuclease functions reside in the carboxy-terminal fragment including residues 62-317. In addition, site-directed mutagenesis identified single amino acid changes that selectively alter or eliminate either the nuclease function or the redox function of Ref-1. By using a transgenic mouse model, it was recently established that mice with a null phenotype for Ref-1 (homozygous for a deleted allele) are inviable; hemizygous mice carrying one wild-type allele are viable and appear normal. However, rescue of the Ref-1 null mice has not been reported. A collaboration between Drs. Samuel H. Wilson and Robert Sobel (NIEHS) and myself has been initiated to discriminate between the possible causes of the lethal phenotype of Ref-1 knockout mice. The experimental design is to make transgenic mice carrying various alleles of Ref-1 in a wild-type background. These homozygous transgenic strains will then be mated with hemizygous Ref-1 mice, siblings of this cross will be characterized and mated, and the progeny of this mating will be studied.